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Giant Hogweed




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Giant Hogweed Control (Heracleum mantegazzianum)

Urban Nature Consultants has years of experience in the abatement of Giant Hogweed, and extensive knowledge about its biology and the mechanical methods appropriate to its abatement.

Origin of the Plant

Giant Hogweed is a perennial endemic to the Caucasus Region and Central Asia. Because of its height and impressive stature, it was introduced to Europe [1] and North America [2], as an ornamental garden plant in the early 1900s,.

Biology and Seed Dispersal

Giant Hogweed can live for several years and dies after bearing seed [3]. The plant can grow 4 to 5 meters in height with a stem diameter of 10 centimetres. Each flowering plant can produce approximately 20,000 seeds [4], and the majority fall close to the parent. However, depending on the location of the plant population, there are other means of seed dispersal. If the population is located on a stream bank or close to roads and highways, there is potential for the seeds to be dispersed long distances. Abatement methods consider location, biology and life stage of the population.

There will be a large "seed bank" due to the thousands of seeds a single plant can produce. 95% of the seed will be concentrated in the top 5 cm of soil. In the autumn, a seed bank can contain up to 12,000 seeds/m2. However, the majority will die in winter. By spring, about 2,000 seeds/m2 remain ready to germinate, and about 5% will survive in the seed bank until the following spring [5].

Abatement methods

UNC only uses mechanical methods, which depend on the life stage, location of the individual populations and the status and usage of the infected area.

  • Cutting off the umbels with a scythe is necessary if there are flowering plants in the population. It is important to make sure that the umbel does not ripen its seed once cut. When the umbel has been cut off, the plant produces "panic umbels", making it necessary to inspect an area several times during the flowering period.
  • Digging up the roots can be effective depending on the size of the population, soil type and life stage of the plants.
  • Ploughing can be used if the area infected is not of a "high nature value". Ploughing has to be repeated several times during the growing season. If there are flowering plants in the population, the umbels have to be cut off before ploughing, to make sure the seeds do not spread and/or make contact with the soil [6].
  • Grazing can be used in areas that cannot be ploughed due to environmental legislation, or where the population is too large and digging is inconvenient. Grazing pressure should be moderate to high to make sure the plants are suppressed throughout the growing season [7]. Grazing must be continued for several years and the area checked regularly for flowering umbels.

Abatement of Giant Hogweed takes several years, and much patience. Best practices and follow up are essential components of mechanical eradication.

What We Offer

Management plans for the abatement of invasive species begins with mapping the infected areas. Individual populations of invasive species are located and best practices suggested. UNC only recommends mechanical abatement methods and does not use pesticides.

UNC also holds seminars for civic workers, landowners and/or volunteers outlining best practices in the abatement of Giant Hogweed. The seminars also deals with health and safety issues.

Please contact UNC to arrange a meeting.

The Giant Hogweed Best Practice Manual
[2] Giant Hogweed: an invasive species causes
[3] The Giant Hogweed Best Practice Manual
[4] Praktisk bekæmpelse af bjørneklo
[5] The Giant Hogweed Best Practice Manual
[6] Praktisk bekæmpelse af bjørneklo
[7] Praktisk bekæmpelse af bjørneklo

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